The present invention relates to an improved method for producing soy protein products having a high concentration of both soluble protein and solubilized carbohydrate and being further characterized by freedom from activity of micro-organisms, absence of objectionable soybeam flavor, suitability for use in food preparations for human consumption, enhanced palatability, and ease of dispersibility and suspension stability in aqueous systems. The products produced in accordance with the invention are especially useful as adjuncts in food products, including meat products.
More particularly, the invention is directed to a method for treating aqueous slurries of soybeam material in accordance with a unique, unobvious, and most fruitful combination of controlled processing steps in which such parameters as pH, treatment temperature and time, neutralization steps, and cooling are precisely regulated so as to effectuate the aims and objects of the invention which will become apparent upon consideration of the following specification. In subject matter, the present invention is related to Sair and Melcer U.S. Pat. No. 3,699,677. The instant innvention is believed to constitute a significant improvement over the method there set forth. Because of its relevance, the entire disclosure of U.S. Pat. No. 3,699,677 is hereby specifically incorporated by reference, to the extent that it is not inconsistent herewith.
The above-identified U.S. Pat. No. 3,669,677 has as a principal goal the reduction of the bacterial count in proteinaceous materials derived from soybean sources. The process there set forth comprises raising the temperature of a slurry of defatted and water-extracted isoelectric (pH 4 to 5.5) soybean material up to at lest about 160.degree. F and preferably up to about 180.degree. or 190.degree. to 212.degree. F, holding the slurry at the elevated temperature for at least about 10 minutes, and then raising the pH of the slurry from an isoelectric pH to a pH of from about 6 to about 10.5. While the above described process has been found capable of providing a soybean protein product having a thermophile count of less than 300 per gram, and a total bacterial count of less than 25,000 per gram, there has been continued concern and interest in producing soy products having even lower concentrations of viable micro-organisms.
The instant invention stems from research carried out initially for the principal purpose of developing a soybean protein product substantially free of micro-organisms. It was in the conduct of the research referred to that several important unexpected and unobvious discoveries were made relating to improvements in the physical and chemical properties and in the composition of soybean-derived proteinaceous materials.
The bacterial content of goods and food ingredients is of special importance in our present society. For many of the foods being prepackaged, stability and safety in use are related directly to bacterial content. The problem of controlling bacteria in such foods has been one of long conern and many techniques have been proposed for accomplishing the intended goal. For example, Lloyd A. Hall U.S. Pat. No. 2,107,697 and U.S. Pat. No. Re.22,284 describe the utilization of a gas sterilization technique involving vacuum treatment of food materials followed by exposure to ethylene oxide. While this process was found to be extremely effective, other considerations preclude its general use. Another technique for controlling bacterial content involves application of dry heat. However, such processes are limited in utility.
In the wet processing of soybean materials, the potential for bacterial growth is a serious problem. In wet-milling of corn, sulfite has traditionally been used as an aid in controlling bacterial growth. But the end uses of soy concentrate and isolates, especially in meat applications preclude the use of substantial concentration of sulfite during wet processing.
In the manufacture of an isoelectric washed soy protein concentrate (see Sair U.S. Pat. No. 2,881,076), the soy flour is suspended in water and acid then added to a pH of 4.0, in the presence of a low concentration of sulfite. This produce is then dewatered, washed repeatedly, and finally neutralized and spray dried. In the commercial production, such processes must continue for days, during which time there is always the potential for bacterial build up.
A patent of Sair and Melcer, U.S. Pat. No. 3,699,677, details a procedure which more effectively reduces the bacterial content of a spray dried soy protein concentrate. Following the procedure there set forth, in order to obtain an effective bacterial kill, even in the isoelectric pH range (approximately pH 4.0 to 5.0), a temperature of at least 180.degree. F is required. Even at this elevated temperature, with a 60-minute heating period, it was not possible to reduce the thermophiles to a value of less than 2 per gram. Only by raising the temperature to 200.degree. F was it possible effectively to destroy the bacteria within a reasonable time. Moreover, the utilization of such a temperature in commercial operations, in accordance with the technique of U.S. Pat. No. 3,669,677 posed temperature-related difficulties due in part to proximity to the boiling state. The procedure was somewhat marginal, with sporadic results. Thermophiles were not always adequately destroyed. Moreover, at this high temperature, under the conditions set forth, nitrogen solubility of the protein component of the soy product was reduced. Such deficiencies are objectionable since a principal processing goal is to provide proteinaceous materials of high protein solubility, and associated good emulsion capabilities.